BACKGROUND Germ cell formation has been investigated in sessile forms of tunicates. This process involves the release of a subset of maternal transcripts from the centrosome-attracting body (CAB) in the progenitor cells of the germ line. When germ-soma segregation is completed, CAB structures are missing from the newly formed primordial germ cells (PGCs). In free-swimming tunicates, knowledge about germ cell formation is lacking. In this investigation, comparative gene expression and electron microscopy studies were used to address germ cell formation in Oikopleura dioica (O. dioica). RESULTS We found that the RNA localization pattern of pumilio (pum1) is similar to the pattern described for a subset of maternal transcripts marking the posterior end of ascidian embryos. Transcripts marking the posterior end are called postplasmic or posterior-end mark (PEM) transcripts. We found no localization of vasa (vas) transcripts to any sub-region within the germ-line precursor cells. Expression of vas4 was detected in the newly formed PGCs. Electron microscopy studies confirmed the presence of structures with similar morphology to CAB. In the same cytoplasmic compartment, we also identified pum1 transcripts and an epitope recognized by an antibody to histone H3 phosphorylated on serine 28. CONCLUSIONS Our findings support that a CAB-like structure participates in the segregation of maternal pum1 transcripts during germ-soma separation in O. dioica.

中文翻译：

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在urochordate Oikopleura dioica早期发育过程中，胚芽-体分离中存在吸引中心体的结构样的证据。

背景技术已经以无柄的被膜形式研究了生殖细胞的形成。此过程涉及从生殖系祖细胞中的吸引中心体（CAB）释放一部分母本转录物。生殖－生殖间分离完成后，新形成的原始生殖细胞（PGC）中缺少CAB结构。在自由游泳的外衣中，缺乏关于生殖细胞形成的知识。在这项研究中，比较基因表达和电子显微镜研究被用来解决Oikopleura dioica（O. dioica）中生殖细胞的形成。结果我们发现pumilio（pum1）的RNA定位模式与描述了标记海鞘胚胎后端的母本转录子的模式相似。标记后端的转录本称为后质或后端标记（PEM）转录本。我们没有发现vasa（vas）转录本定位到种系前体细胞内的任何子区域。在新形成的PGC中检测到vas4的表达。电子显微镜研究证实存在与CAB形态相似的结构。在同一个细胞质区室中，我们还鉴定了pum1转录物和被丝氨酸28磷酸化的组蛋白H3抗体识别的表位。结论我们的发现支持CAB样结构参与母体pum1转录物在细菌分离过程中的分离。 O. dioica。在新形成的PGC中检测到vas4的表达。电子显微镜研究证实存在与CAB形态相似的结构。在同一个细胞质区室中，我们还鉴定了pum1转录物和被丝氨酸28磷酸化的组蛋白H3抗体识别的表位。结论我们的发现支持CAB样结构参与母体pum1转录物在细菌分离过程中的分离。 O. dioica。在新形成的PGC中检测到vas4的表达。电子显微镜研究证实存在与CAB形态相似的结构。在同一个细胞质区室中，我们还鉴定了pum1转录物和被丝氨酸28磷酸化的组蛋白H3抗体识别的表位。结论我们的发现支持CAB样结构参与母体pum1转录物在细菌分离过程中的分离。 O. dioica。